Polymers of ethylene oxide have heretofore been produced in two molecular weight ranges. Those whose maximum molecular weight is about 20,000 to 30,000 are called “polyethylene glycol.” Examples of non-patent documents dealing with such material include K. C. Frisch et al.: “Ring Opening Polymerization”, New York, Marcel Dekker (1969) and T. Saegusa: “Ring Opening Polymerization”, Washington, published by Am. Chem. Soc., 1977.
On the other hand, ethylene oxide polymers having a molecular weight of about several hundreds of thousands to about 8,000,000 are referred to as “poly (ethylene oxide).” Examples of patent documents in which such a technology is disclosed include U.S. Patent Specification No. 2971988, JP-B No. S45-7751 and JP-B No. S53-27319.
Documents concerning ethylene oxide polymers are fraught with much confusion. The two terms, polyethylene glycol and poly(ethylene oxide), are often used exchangeably. In Chemical Abstracts, there is, in fact, only one index number for polymers of ethylene oxide. It has been considered that those of only two different molecular weight ranges can be produced and a significant difference in that those are produced by quite different methods has not been recognized.
One of the methods is, as already stated, able to produce only those having a maximum molecular weight between about 10,000 and 30,000. The other method is able to produce only those having a maximum molecular weight between about 100,000 and 900,000 and those having a minimum molecular weight of 900,000 or more. It, therefore, is apparent that it was impossible to produce ethylene oxide polymers having molecular weights not less than about 30,000 and not more than about 100,000. When taking account of many applications of such polymers having medium molecular weights, there is a wide requirement for eliminating the existing molecular weight gap.
Ethylene oxide polymers having molecular weights within the range of several hundreds of thousands or more normally have a very wide molecular weight distribution and it is true that it is difficult to control their molecular weight during their production.
Furthermore, it is very difficult to produce ethylene oxide polymers having molecular weights of 100,000 or more economically in high yields. The method generally known in the art is to reduce the molecular weight of a polymer initially produced so as to have a molecular weight of 1,000,000 or more by gamma-ray irradiation in order to obtain a polymer having a desired molecular weight within the range of 100,000 to 900,000.
Therefore, there is a demand for ethylene oxide polymers having molecular weights within the range of not less than about 10,000 to 30,000 and not more than about 100,000, which is a range having not been achieved. However, no suitable catalysts capable of achieving such a result have been disclosed.
The object of the present invention is to provide a polymerization catalyst composition capable of producing a poly(ethylene oxide) polymer having a molecular weight range from about 20,000 to 200,000 by direct polymerization economically in a high yield and a method for the production of a poly (ethylene oxide) polymer utilizing the polymerization catalyst composition.
The present inventors studied diligently to solve the above-mentioned problems. As a result, we found that when a specific polymerization catalyst composition is used in the production of poly (ethylene oxide) by directly polymerization of ethylene oxide, the polymerization of ethylene oxide proceeds extremely satisfactorily and the molecular weight distribution becomes very sharp and, therefore, the molecular weight of the resulting polymer can be controlled within a specific range. Thus, the inventors have accomplished the present invention.